Store size for chunk in config.chunks.

Mongo currently will sometimes not shard chunks and we have seen 200M, 2000M 20000M chunks at times. To avoid this anytime a migration or split occurs mongo should update the chunks "size" into the config.chunks documents. This would make it easier to correct this , since jumbo is not ALWAYS set correctly.

The result is we could have tools to correct chunks until such time chunk splitting is moved to the mongod nodes, and possible even then if similar issue with detect still occur.